The vectorcardiogram in dorsal or posterior myocardial infarction

Abstract

The vectorcardiograms of twenty-five patients with dorsal infarction of the heart were studied. These infarctions were classified into four groups as follows, all of which showed an increase of the R wave in the B (anterior-posterior) component of Grishman's cube system: 1. 1. Strictly dorsal infarction, showing only an increase of the R wave in the B component. In this group were three cases, including one complicated by complete right bundle branch block. 2. 2. Inferodorsal infarction, showing pathologic Q waves in the C (superior-inferior) component. There were five cases in this class. 3. 3. Laterodorsal infarction, showing abnormal Q waves in the A (right-left) component. Eight cases were placed in this class. 4. 4. Inferolaterodorsal infarction, with abnormal Q waves in the A and C components. There were nine cases, including two complicated by complete right bundle branch block, in this group. The vectorcardiograms of these cases showed increased magnitude and forward orientation of the initial portions (0.02 second) of the ventricular activation loop. These initial portions frequently had a higher speed of inscription due to the absence of opposing forces. The necrotic areas in the dorsal wall which should undergo early depolarization were not activated at the same time; therefore, no electrical forces were produced in those areas. In dorsal infarction, the rotation of the QRSsÊ in the horizontal plane was predominantly counterclockwise. This, together with the direction of predominant forces forward (average 0.048 second) and the orientation of the TsÊ in the same direction, facilitates the diagnosis of dorsal infarction in those cases in which a tall R wave in the right precordial leads might suggest right ventricular hypertrophy. In eleven cases a certain delay of inscription and deformity in the morphology of the terminal portions of the QRS loop was observed.